1. Field of the Invention
The present invention relates generally to machines for forming glassware articles from gobs of molten glass and in particular to safety controls for electronically controlled individual section glassware forming machines.
2. Description of the Prior Art
The individual section or IS glassware forming machine is well known and includes a plurality of sections each having means for forming glassware articles in a timed, predetermined sequence of steps. Typically, each section includes a blank mold station for receiving gobs of molten glass at a predetermined rate and for partially forming articles of glassware. A partially formed article of glassware of the type produced by the blank mold is typically referred to as a parison. The parison is then transferred to a blow mold station wherein the formation of the glassware articles is completed. The sections are operated in synchronism at a relative phase difference such that one section is receiving a gob while another section is delivering a finished glassware article to a conveyor and one or more other sections are performing various ones of the intermediate forming steps.
The forming means in each section are typically operated from pneumatic motors or actuators. In early prior art machines, the pneumatic motors were controlled by a valve block which in turn was controlled by a timing drum for each section driven from a line shaft which synchronized all parts of the machine. Manually adjustable cams were positioned on the timing drum for actuating the valves in the valve block. Timing was adjusted by loosening, moving and tightening the cams as the drum rotated.
One of limitations of the timing drum was the difficulty of adjusting the timing during the operation of the machine. One solution to this problem was to replace all the timing drums with an electronic control means. The electronic control means included a master unit which was responsive to a clock pulse generator and to a reset pulse generator both driven by the line shaft. The master unit generated reset signals to a separate control circuit for each of the individual sections to synchronize the operation of the individual circuits. Each control circuit included a pulse counter responsive to the clock pulses and the master unit generated reset pulses for counting the degrees of the section cycle. Each individual circuit included forty-eight, three-decade thumbwheel switches for setting the degree of rotation of the machine thereon. Thus, each particular function of the glassware forming cycle was controlled by one of the thumbwheel switches. Such a control system is disclosed in U.S. Pat. No. 3,762,907.
The previously described electronic control system utilized discrete components in its counter gating circuitry. In a later prior art control apparatus, a digital computer with a timing data memory and associated program storage was utilized. Not only did such a control circuit provide a means for automatically changing the timing values of the functions without the manual resetting of thumbwheel switches, but such a circuit also provided a means for programming events, groups of related functions, in accordance with certain boundary event timings. The computer generated the control signals through an interface circuit to actuate solenoid controlled valve blocks. Such a control system is disclosed in U.S. Pat. No. 3,905,793.
Typically, the prior art control systems had means for automatically performing a sequence of steps for moving the glassware forming mechanisms into positions for operation in a normal operating cycle. This was known as a programmed start. The prior art control systems also included means for initiating an emergency stop or a programmed stop. The emergency stop was effective at any time to immediately stop the machine and to release anything caught in the molds, the neck ring, or the blow head. The programmed stop was only effective during a normal operating cycle to automatically perform a sequence of steps for moving the glassware forming mechanisms into positions for ease of maintenance. The prior art control systems functioned to initiate an emergency stop if the programmed stop switch was actuated during a programmed start. One problems with the prior art control systems was the possibility that the machine could automatically restart upon the release of the emergency stop switch. If the programmed start circuitry malfunctioned so as to remain in the "on" condition, the release of the emergency stop switch, or the entry into a safe condition from a programmed stop or a sample routine, would cause the machine to enter the programmed start which could be dangerous to the operator or a maintenance person.